The art of measuring light transmissivity in a work piece is relatively well known. In general, light from a source passes from a front side of the work piece to the backside where a detector collects it. The difference between the light irradiated towards the work piece and the light that actually passes through the work piece, as collected by the detector, corresponds to the work piece transmissivity.
Problems arise, however, because the light source, often a white light source, illuminates the front of the work piece with multiple wavelengths while the detector only collects light at its tuned wavelength. This can unnecessarily limit measurement of multiple wavelengths to incorporating multiple detectors. Additionally, typical commercial transmissivity measurement devices lack sufficient irradiation power to penetrate work pieces and project light to backside detectors when the work pieces embody other than visibly clear compositions. Traditional visibly clear compositions include glass, quartz, polycarbonate, polystyrene, and the like. They usually also lack sufficient power to project light through work pieces, such as high impact polystyrene and polyester having typically low transmissivity characteristics.
Accordingly, the arts for measuring light transmissivity desire solutions for overcoming the aforementioned and other problems.
Numerous reasons exist for understanding light transmissivity in a work piece. For example, consider instances when two work pieces undergo laser welding. As background, first and second work pieces become welded to one another by way of a fixed or sweeping irradiated beam of laser light. As is known, the beam passes through the first work piece, which is transparent to laser light, where it gets absorbed by the second work piece, which is laser light absorbent. As the beam irradiates, the weld interface heats-up which causes the adjoining surfaces of the work pieces to melt. Upon cooling, the two work pieces meld together as one.
Yet, if the first work piece prevents sufficient amounts of laser light from reaching the weld interface, poor welding (underweld) results. Further, if the first work piece absorbs too much energy, the first work piece may overheat and/or suffer material degradation potentially causing poor weld appearance or unsatisfactory welds. Numerous parameters contribute to the absorption and transmission characteristics of a work piece including, but not limited to, laser wavelength, incident angle of the laser beam during welding, surface roughness of the work piece, temperature of the work pieces, thickness/dimensions of the work piece, composition of the work piece and, in instance when work pieces comprise plastics, additives such as flame retardants, plasticizers, fillers and colorants.
When the material properties and laser properties become fixed in a given system, however, the transmission rate of the laser through a work piece follows the well known Beer-Lambert Law, specifically: I/Io=e(−sx); where Io is the intensity of the light source incident on the work piece, I is the intensity of the light after passing through the work piece, x is the thickness of the work piece, and s is the total extinction coefficient which, in turn, is the work piece light scattering coefficient plus the work piece light absorption coefficient. Accordingly, the transmissivity of the work piece constitutes an important variable (underscored by the ratio I/Io) in light transmission rates.
As such, those skilled in the laser welding arts will appreciate that having an ability to assess, predict or otherwise identify a laser light transmissivity characteristic of a work piece before the piece undergoes welding will likely significantly decrease failure weld-rates in to-be-welded work pieces.
Accordingly, a need exists in the laser welding arts for efficaciously predicting and identifying laser light transmissivity in to-be-welded regions of a work piece.
Regarding the technology of inkjet printing, it too is relatively well known. In general, an image is produced by emitting ink drops from an inkjet printhead at precise moments such that they impact a print medium, such as a sheet of paper, at a desired location. The printhead is supported by a movable print carriage within a device, such as an inkjet printer, and is caused to reciprocate relative to an advancing print medium and emit ink drops at such times pursuant to commands of a microprocessor or other controller. The timing of the ink drop emissions corresponds to a pattern of pixels of the image being printed. Other than printers, familiar devices incorporating inkjet technology include fax machines, all-in-ones, photo printers, and graphics plotters, to name a few.
A conventional thermal inkjet printhead includes access to a local or remote supply of color or mono ink, a heater chip, a nozzle or orifice plate attached to the heater chip, and an input/output connector, such as a tape automated bond (TAB) circuit, for electrically connecting the heater chip to the printer during use. The heater chip, in turn, typically includes a plurality of thin film resistors or heaters fabricated by deposition, masking and etching techniques on a substrate such as silicon.
To print or emit a single drop of ink, an individual heater is uniquely addressed with a small amount of current to rapidly heat a small volume of ink. This causes the ink to vaporize in a local ink chamber (between the heater and nozzle plate) and be ejected through and projected by the nozzle plate towards the print medium.
During manufacturing of the printheads, a printhead body gets stuffed with a back pressure device, such as a foam insert, and saturated with mono or color ink. A lid welds to the body via ultrasonic vibration. This, however, sometimes causes cracks in the heater chip, introduces and entrains air bubbles in the ink and compromises overall integrity.
Even further, as demands for higher resolution and increased printing speed continue, heater chips become engineered with more complex and denser heater configurations which raises printhead costs. Simultaneously, the heater chips become smaller and flimsier to save silicon costs. Thus, as printheads evolve, a need exists to control overall costs and to reliably and consistently manufacture a printhead without causing cracking of the ever valuable heater chip.